Physiological and Yield Variability Among the Elite Rice Germplasm.

Rice is the most important crop that provide calories to over half of the global population. It is grown under different climates where environmental conditions vary substantially. Identifying genetic variability for physiological and yield traits will have implications for selecting lines for improving yield traits through breeding. An experiment was conducted to investigate morpho-physiological traits at 90 days after sowing and yield and yield-related traits at maturity for 100 elite rice genotypes comprised of advanced breeding lines and released varieties. All plants were grown in a sunlit, pot-culture facility with optimum water and nutrient conditions throughout the experiment. Rice lines varied significantly for many of the traits measured. The individual vigor response index estimated for a given trait was calculated as the ratio of the trait values by maximum value among the lines. Cumulative vigor response index (CVRI) was calculated by summing up all indices of measured traits for each rice line. Cumulative vigor response index and one standard deviation were used to classify the rice lines into different groups. The CVRI varied from 13.755 (RU1104122) to 15.314 (RU1504083). Based on this method, four groups were identified; two as very low, 30 as low, 32 as moderately low, 28 moderately high, and 7 as high vigor groups among the 100 lines tested. The significant and positive correlation between final harvest CVRI and physiological trait vigor index (r² = 0. 88) measured a few days after flowering implies that physiological traits could be used to characterize vigor indices among the rice genotypes. The identified CVRI values for various lines will be useful in rice breeding programs to select and develop new genotypes with greater vigor and yield.